Hollow particles of metal oxides are expected to contribute to improvement in catalytic functions and the realization of a new function. For example, Patent Document 1 discloses that hollow particles of titanium oxide are produced by adding a toluene solution of titanium butoxide to an ionic liquid and vigorously stirring the resultant mixture. This is described as follows: The titanium oxide hollow particles are formed by sol-gel reaction of the titanium butoxide due to a trace amount of water in the ionic liquid at the interfaces of toluene microdroplets formed in the ionic liquid. In addition, Patent Document 2 discloses a method for producing a hollow oxide shell structure by alternately adsorbing a nano-sheet of layered oxide and a cationic polymer in a liquid phase on a polymer sphere to form a multilayer thin film including the nano-sheet and the cationic polymer on the polymer sphere, and then removing the polymer sphere. On the other hand, Non-Patent Document 1 reports that as a result of TEM (Transmission Electron Microscope) observation of a change in shape of Cu nanoparticles after oxidation at room temperature to 400° C., hollow nanoparticles were formed by oxidation.
Patent Document 1: JP 2004-035303 A
Patent Document 2: JP 2004-130429 A
Non-Patent Document 1: Catalyst, Vol. 49, No. 5, 2007, pp. 344-349